The slider shown in EP 1 057 423 A1 and EP 1 175 842 A1 incorporates a guide plate or “guide flange” in the form of a thin blade which projects from the wedge or guide post which joins the upper and lower wings of the slider. This guide plate extends between the outer ends of the coupling elements and the sealing lips. Thus the guide plate creates upper and lower paths within the slider and serves to ensure more accurate alignment of the coupling elements as they are brought together and enables greater pressure to be exerted on the sealing lips whilst keeping them aligned.
In practice, the slider shown in EP 1 057 423 A1 and EP 1 175 842 A1 has been made of three parts, with the guide plate being formed separately and sandwiched between the upper and lower wings and guide post portions on each wing. This adds significantly to the cost of the production process.
EP 1 900 297 A1 describes an integrally formed slider. In particular the slider may be die cast or moulded as a single, integral member of metal or plastics material. By integrally forming the slider, the slider is stronger, particularly in the region between the upper plate and the guide plate where the slider parts are subject to greater separation forces as the slider is pulled along the fastener to urge the sealing lips together. This substantially reduces the cost of the production process and also leads to an improvement in product quality because of the avoidance of any misalignment or other errors which may arise in an assembly process.
A difficulty with the prior art slider design was the use of a relatively thin guide plate which extended a relatively long distance from the guide post and so was unsupported. This could not be reliably moulded as an integral part of the slider.
Although the guide plate in EP 1 900 297 A1 is shaped to provide a thicker guide plate and also a smooth path for the sealing lips, there are still difficulties in ensuring that the slide fastener tapes always mate properly to form a good seal. For example the sealing lips may slip out from between the upper and lower wings of the slider or the coils may slide up alongside the edge of the guide plate.